A medical diagnosis using an endoscope has been common in the medical field. The endoscope has an insertion section and an operating section. The insertion section is inserted in a body cavity. The operating section is provided at a base end of the insertion section. A distal tip of the insertion section is a rigid portion incorporating an image taking device having an imaging element such as a CCD. Image signals taken by the CCD are subject to signal processing in a processor. Thereby, images in the body cavity are observed on a monitor or the like. The insertion section is provided with a forceps channel through which a medical instrument (treatment instrument) is inserted into the body cavity. Such medical instrument is used for performing a biopsy of affected tissue, or the like, while images of the inside of the body cavity are observed.
At a base end of the rigid portion is provided a bending portion in which plural (for example, 16) joint rings are connected in series. Each joint ring has a cylindrical body, a pair of outer projections, and a pair of inner projections. The outer projections extend out from one side of the cylindrical body in an axis direction of the insertion section. The inner projections extend out from the other side of the cylindrical body in the axis direction. The outer projection and the inner projection are shifted from each other by 90° in a circumferential direction of the cylindrical body. A coupling hole is formed to penetrate each of the inner and outer projections. The outer projection and the inner projection of the adjacent joint rings are overlapped and coupled rotatably with a coupling pin which is inserted through the coupling holes. Two pairs of operation wires are provided along in the joint rings for moving the joint rings in an up-and-down direction and a right-and-left direction. Pushing or pulling the operation wires rotates the joint rings and bends the bending portion.
The operating section is provided with an angle knob for pushing or pulling the operation wires. The bending portion is bent in the up-and-down direction or the right-and-left direction by operating the angle knob. Thus, the rigid portion is directed to a desired direction.
Various attempts have been made to reduce a diameter of the insertion section of the conventional endoscope configured as above. For example, in Japanese Patent Laid-Open Publication No. 2001-128937, a signal cable in which signal lines extending from an imaging device are bound together is split into plural signal cables. Of those, the signal cable having the largest diameter is disposed within or close to a space having the largest diameter between an outer perimeter of a forceps channel and an inner circumferential surface of an insertion section. The forceps channel has the largest outer diameter among internal components arranged within the insertion section. The outer diameters of the signal cable having the largest diameter and the rest of the signal cables are set so as to make an inner diameter of the space, in which the signal cables are arranged, a minimum.
In Japanese Patent No. 3590199, operation wires for bending a bending portion are branched. Such branched operation wires are arranged so as not to come in contact with other internal components.
Such attempts reduced the diameter of the insertion section, which replaced the conventional oral endoscope adapted to be inserted through a mouth with a nasal endoscope adapted to be inserted through a nostril. The diameter of the insertion section of the nasal endoscope is at most 6 mm.
The joint rings are necessary for the bending portion regardless of whether it is an oral endoscope or a nasal endoscope. A diameter of the insertion section is determined based on a diameter of the bending portion. For example, as shown in FIG. 9, coupling pins 103 for coupling adjacent joint rings 101 are disposed in a bending portion 102 constituted with joint rings 101. For this reason, it is necessary to arrange internal components in the joint rings 101 such that the internal components don't come in contact with the coupling pins 103. Therefore, an arrangement of the internal components in the bending portion 102 is a key factor for reducing the diameter of the insertion section. The bending portion 102 has a configuration in which a forceps channel 104, optical fibers 105 as a light guide, an air/water channel 106, a signal line 107, and the like are arranged. The forceps channel 104 has the largest diameter among the above-mentioned internal components in the bending portion 102, and is disposed at the center of the joint rings 101 in the diameter direction. The optical fibers 105, the air/water channel 106, the signal line 107, and the like are disposed around the forceps channel 104 and contact with inner circumferential surfaces of the joint rings 101 while they are kept away from the coupling pins 103. An operation wire 109 used for bending the bending portion 102 is threaded through a guide hole 108 formed in the coupling pin 103.
As shown in FIG. 9, diameters of the optical fibers 105 and the signal line 107 are reduced by virtue of the selection of materials. On the other hand, the diameter of the air/water channel 106 is still large relative to the optical fibers 105 and the signal line 107. Therefore, improvements in the arrangement of the air/water channel 106 would further reduce the diameter of the insertion section. Although Japanese Patent Laid-Open Publication No. 2001-128937 and Japanese Patent No. 3590199 disclose to reduce the diameter of the insertion section by splitting the signal line or the operation wire, there are no improvements on the air/water channel and no significant solutions to reduce the diameter of the air/water channel. In addition, in the method disclosed in Japanese Patent No. 3590199, the operation wire may break due to stress concentration at a branch point of the operation wire, resulting in medical accidents.